 
#include<iostream>
using namespace std;
const int MAX = 1010;
bool vis[MAX];

int main() {
    int n, m;
    cin >> n >> m;
    cout << n - m << endl;
    for (int i = 1; i <= m; ++i) {
        int a;
        cin >> a;
        vis[a] = true;
    }
    for (int i = 1; i <= n; ++i) {
        if (!vis[i])
            cout << i << " ";
    }
    cout << endl;
    return 0;
}
 